Many research studies have demonstrated that a regular physical exercise/activity program helps our bodies reduce the risk of chronic health conditions ranging from heart disease to cancer to diabetes. Despite the overwhelming and unambiguous health benefits of a regular exercise program, a significant percentage of our population is considered physically inactive or sedentary. When looking at reasons why sedentary individuals don’t exercise regularly, a common answer given is that the time and effort to engage in a traditional exercise program feels too daunting.
With this in mind, we’d like to bring your attention to a study which evaluated the effectiveness of a low-volume, high-intensity interval training program in generating meaningful improvements in the metabolic performance of sedentary adults. 
Why, you might ask, is this worthy of your attention? Well, as the study authors explained:
“Despite the beneficial effect of endurance exercise training on cardiorespiratory and metabolic health, many individuals consider its lengthy time requirement a barrier to performing regular exercise. Therefore, less time consuming interventions may be more attractive. We and others have demonstrated that HIT (high-intensity interval trainings) is a potent stimulus to elicit adaptations that resemble those of traditional endurance training despite a substantial reduction in the total time commitment and exercise volume. Direct comparisons of low-volume HIT and traditional high-volume endurance training suggest that both protocols lead to similar increases in muscle mitochondrial content and endurance exercise performance.
Low-volume HIT also rapidly increases skeletal muscle glucose transporter (GLUT4) protein content. Two studies also reported a significant improvement in insulin sensitivity following 2 wk of HIT.”
In other words, low-volume, high-intensity interval training might be a reasonable alternative for people who struggle to start and maintain a regular exercise program because of the time commitment required. Many popular exercise programs recommend 60-90 minutes of cardiovascular and/or resistance training four to five days a week while this study’s training regimen showed noteworthy metabolism benefits from 20 minutes of exercise three days a week.
The metabolism indicators evaluated in the study include muscle oxidative capacity (the amount of oxygen a muscle can utilize during physical activity) and insulin sensitivity (how receptive the muscle cells are to accept insulin’s transport of glucose into the cell to help produce energy). The study team selected these markers because they are typically found to be depressed in sedentary individuals.
The mechanism at work here is as follows: Let’s say you want to get up, walk across the room and answer the phone. To accomplish this act, your brain sends signals to muscle cells indicating a demand for muscle movement. In turn, the muscle cells send out signals indicating a need for glucose to help produce energy in order to facilitate the muscle movement (some glucose is floating freely in the blood and some is stored in the form of fat cells). The recipient of the muscle cells’ call for glucose is the pancreas, which produces a facilitator molecule called insulin. Insulin’s job in this chain reaction is to seek out glucose, grab hold of it and hand deliver it to the muscle cells. When insulin molecules with glucose molecules in tow show up at the muscle cells, they are supposed to signal the muscle cell wall to open up and accept the glucose molecule. Once the glucose is absorbed into the cell, it is converted into energy by the cells mitochondria, allowing the muscle to react to the brain’s command.
That’s how it is supposed to work. But in sedentary individuals, this process is often disrupted. In particular, two things seem to happen when we don’t regularly engage in physical activity. First, muscle cells become “insulin resistant,” meaning they either don’t recognize that insulin has arrived bearing glucose or they don’t open up and allow the glucose in. This results in an oversupply of both free-floating glucose and insulin in our blood. Since the muscle cells aren’t getting the glucose they need, they keep sending out signals for more glucose, which means the pancreas creates more and more insulin.
The second effect of this process breaking down is reduced muscle oxygen capacity. You see, the muscle cells not only need glucose to produce energy, they also need oxygen delivered from the lungs via red blood cells. Without both pieces delivered in the appropriate mix, the muscle cells can’t utilize the oxygen that has arrived. It’s similar to how a combustion engine works in an automobile — air is mixed with fuel in the engine cylinders, and when an electrical spark is introduced by a spark plug an internal explosion is triggered, which provides the energy for the car to move. An inappropriate mix of fuel and air will cause a car engine to misfire and/or operate inefficiently. In human muscle cells, the inappropriate mix of glucose and oxygen reduces the cells’ capacity to utilize oxygen efficiently.
The amazing thing about regular exercise is that it appears to help re-sync the body’s energy transport/utilization process (i.e., metabolism). In other words, exercise appears to help the body self-correct how it produces and uses energy though scientists don’t fully understand how or why. And low-volume, high-intensity interval training might just provide an interesting alternative to help this “reset” process.
What is Low-Volume, High-Intensity Interval Training?
Low volume in this context means a short exercise session duration (a 20-minute workout versus a 60-minute workout) and fewer weekly exercise sessions (three days per week versus five or more). High-intensity interval training is an approach where one pushes oneself to near maximum effort for repeated short bouts of time (60 seconds) with short bouts of low-intensity exercise or rest in between (60 seconds).
In this particular study, the researchers enrolled seven individuals (four men, three women) with an average age of 45, a body mass index of 27 (categorized as overweight but not obese), who were sedentary (meaning they had not participated in a regular exercise program for at least one year prior to the study), and had no medical contraindications implying a high-intensity exercise program might be inappropriate.
Prior to the study commencing and again at the end, the researchers drew blood samples and performed leg muscle cell biopsies in order to assess changes in metabolism indicators such as muscle oxidative capacity and insulin sensitivity.
The exercise regimen followed by the study participants was described by the researchers as follows:
- Six sessions of high-intensity interval exercise on a cycle ergometer (i.e., stationary bike) over a two-week period, with each session interspersed by one to two days of recovery (i.e., training occurred on Monday, Wednesday and Friday of each week).
- Each session consisted of a three-minute warm-up at 50 W, followed by a series of 10 60-second high-intensity cycling efforts interspersed with 60 seconds of recovery, and terminated with a five-minute cool-down at 50 W.
- The workload during each interval was set at 60% of peak power achieved during a peak test. Mean power output during training was approximately 150 W, and this elicited approximately 80% of heart rate reserve (HRR) at the end of the first 60-second interval, climbing to approximately 95% of HRR after the last interval. During recovery between the high-intensity efforts, subjects cycled at a fixed resistance of 30 W.
The study results showed that six low-volume, high-intensity interval training sessions (three workouts a week for two weeks) improved muscle oxidative capacity by 260% as measured by the change in a cellular protein associated with energy production in the mitochondria (GLUT4).
In addition, insulin sensitivity improved by 35% as measured by the relationship between fasting insulin concentration and fasting glucose concentration. Regarding the muscle oxidative capacity, the researchers noted the low-volume, high-intensity interval regimen produced similar improvement levels as reported from high-volume endurance training programs.
The researchers concluded:
“In summary, the results of the present investigation demonstrate that low-volume, constant-load HIT rapidly induces skeletal muscle mitochondrial biogenesis, increases GLUT4 content and improves insulin sensitivity in previously sedentary adults. These findings provide novel information regarding the potency of low-volume HIT to improve insulin sensitivity to a similar magnitude as previous research examining higher-volume endurance training. Despite similar metabolic adaptations between this HIT and previous endurance training studies, the time requirement of the present protocol involved [approximately] 20 min per session, totaling [approximately] 60 min per week. Given that lack of time is the most often cited barrier to performing regular exercise, low-volume HIT may represent an alternative to traditional endurance training to help increase exercise participation in the general population. Further research is required to examine the long-term impact of low-volume HIT on metabolic health and chronic disease prevention, but the present results suggest that low-volume HIT may be an effective exercise strategy for the prevention and treatment of insulin resistance and inactivity-related disorders.”
If you are interested in constructing and experimenting with a low-volume, high-intensity interval training program, we’d strongly recommend doing so in consultation with your physician and with the assistance of a certified fitness instructor at a local fitness or community center. Fitness instructors can help you establish your interval program starting intensity and when to boost the intensity of your workout. Their recommendations are most often based on guidelines published by fitness organizations such as the American College of Sports Medicine.
Whether you choose to investigate a low-volume, high-intensity interval training program or not, engaging in a regular regimen of physical activity/exercise can confer similar benefits albeit with a greater time commitment.
 Hood MS, et al. Low-Volume Interval Training Improves Muscle Oxidative Capacity in Sedentary Adults. Medicine & Science in Sports and Exercise. 2011 March 25. [Epub ahead of print]